The 4 C's: Cut
What cuts of diamond are there?
The traditional grading for cut refers to how it affects the luminescence of the gem, but we are going to take it one step further and begin by talking about diamond shape as well. As there are plenty of resources out there already, we found this image on Google images to describe the varying shapes diamonds can be found in.
The most common diamond shape is the round, also known as round brilliant. This is because the shape is optimum for reflection of light and results in a fiery, sparkly diamond. However, the shape of diamond that you choose is also dependent on the preferred style of your fiancé and ring design and there are many factors that cause the fire and sparkle in a diamond (see other articles).
The diamond we chose for our ring had a round brilliant cut. Diamonds are graded by official institutions; GIA, IGI and AGM are some of the more common ones. Graded diamonds are sold with a report which details the exact measurements of the diamond. Our diamond was GIA certified and so we will use this institute as an example.
GIA grades the cut of a diamond into five categories:
Excellent
Very Good
Good
Fair
Poor
The diamonds are sorted into these categories based on seven aspects:
Brightness; the amount of light that is reflected from the diamond
Fire; how the light is dispersed into the colours of the spectrum
Scintillation; the flashes of light (sparkle) when the diamond is moved
Weight Ratio; amount of 'hidden weight' in a diamond relative to its size
Durability; affected by the girdle thickness
Polish; amount of polish on diamond's facets (flat surfaces of the diamond)
Symmetry; symmetry of the diamond's facets
On the GIA report, there is an image of the diamond with its exact proportions. There are five parts of this that you should pay particular attention to; the girdle, table, depth, crown angle and pavilion angle.
The girdle thickness relates to the diamonds durability. If the girdle is too thin, the diamond has a higher likelihood of cracking and chipping. However, if a girdle is too thick, then this adds to the diamonds hidden weight and can make the diamond appear smaller.
A medium - slightly thick girdle is what you should aim for. However, a thicker girdle can be better for certain shapes of diamonds, e.g. marquise cut diamonds, as this can strengthen the narrow points.
The table is the largest facet (flat surface) of a diamond and the is usually noted as the percentage relative to the entire width of the diamond. When light enters the table, it is refracted (directed) onto the other facets of the diamond and allows the diamond to sparkle. If the table is too large, the light cannot refract onto the upper facets well, but if the table is too small, not enough light can enter the diamond.
The ideal table percentage for a round brilliant diamond is between 54 - 57%
The depth of a diamond is calculated by dividing the height of the diamond by the width of the diamond. This results in a depth percentage. If the depth is too shallow, the light will pass through the diamond and leave the bottom half without any sparkle. However, if the diamond is too deep, it can make the diamond appear smaller.
A round brilliant diamond should have a depth percentage of between 61 - 62.5%
The crown and pavilion angles can be said to be the most important of these five measurements as they can have the most impact on the diamond's sparkle and fire. They work together so a slightly steeper crown angle can be complemented by a slightly shallower pavilion angle, and vice versa.
For a round brilliant diamond the crown angle should be between 34 - 35 degrees and the pavilion angle should be between 40.6 and 41 degrees
These dimensions for the "perfect diamond" result from a study by Tolkowsky. He studied which diamonds people preferred and then measured the diamond's cut. This led to the 'Tolkowsky cut', which many consider to be optimum for creating a diamond with the most sparkle and fire.
The Holloway Cut Adviser can be used to help determine if your diamond meets these criteria. Just insert your numbers and click Go! However, this is more of a rejection tool than a selection tool.
A score of between 1 and 2 is best for rings. A score below 1 will usually cause a diamond to be too sparkly and is best reserved for other diamond jewellery, such as earrings.
Our recommendations
Buy a diamond that has been officially certified
Use the Holloway Cut Adviser to eliminate less ideal diamonds
If buying a round brilliant diamond, choose one with a medium - slightly thick girdle
This generally is more important if buying a diamond online. If buying a diamond in person, you can determine how much fire and sparkle it has!
